1. Field of the Invention
The present invention relates to a confocal scanning microscope, and more particularly to a confocal scanning microscope capable of producing a high contrast microscopic image.
2. Description of the Prior Art
The prior art includes optical scanning microscopes which converge a beam of illuminating light to a small light spot, two-dimensionally scan a specimen with the light spot, detect light transmitted through or reflected from as well as fluorescence emitted by the specimen by means of a photodetector, and produce an electric signal carrying an enlarged image of the specimen.
One type of such confocal scanning microscope is constituted so as to converge the illuminating light emitted by a light source to a light spot on the specimen, to cause the light from the specimen to be once again converged to a light spot, and to detect the reconverged light by means of a light detector. Since the confocal scanning microscope constituted in this manner does not require a pinhole to be disposed over the specimen surface, it is easy to fabricate.
As can be seen from the example of this type of confocal microscope disclosed in Japanese Unexamined Patent Publication No. 62(1987)-217218, in its basic structure the microscope consists of a light source for emitting illuminating light, a specimen supporting member for supporting a specimen, a light-projecting optical system for converging the illuminating light to a small light spot on the specimen, a light-receiving optical system for focusing the light from the specimen (the transmitted or reflected light together with fluorescence) as a spot image, a light detector for detecting the spot image, a scanning mechanism for two-dimensionally scanning the specimen with the light spot, and an image reproducing means for reproducing an image from the signal output by the light detector.
In the confocal scanning microscope of this type, it is necessary to converge the illuminating light beam to a point on the surface of or within the specimen with high precision, and for this it is necessary, for example, to fine-adjust the position of the specimen supporting member in the direction of the optical axis.
Since the conventional confocal scanning microscope is able to produce an image signal even when the illuminating light is not precisely focused, however, image reproduction has frequently been conducted in a less than perfectly focused condition. As a result, the microscopic image obtained has frequently suffered from poor contrast.